.epsilon.-caprolactone is a high boiling point liquid with excellent reactivity. .epsilon.-caprolactone is used as a raw material in the preparation of polyesterpolyol, urethane resin and the like. Thus, polyesterpolyol for polyurethane and high molecular weight polyesterpolyol, which are produced from .epsilon.-caprolactone, are used as blending agents to improve the properties of various resins.
When polyesterpolyol obtained from .epsilon.-caprolactone is blended with polyethylene, gloss, transparency and blocking preventive ability are improved. When .epsilon.-caprolactone is blended with polyvinyl chloride, low temperature embrittlement of polyvinyl chloride is improved. However, the properties of .epsilon.-caprolactone, particularly its appearance, including its color and the like, often affect the properties of the blended resins, including, for example, their appearance, weather resistance, and the like.
Various treatments have been used heretofore to improve the properties of .epsilon.-caprolactone. Particularly, repetitious purifying distillation using a 10-30 stage distillation column, preservation under nitrogen atmosphere and addition of a stabilizer such as p-methoxyphenol, tridecylphosphite, 2,6-ditertiary-butyl-r-methylphenol, and the like, have been conducted on .epsilon.-caprolactone to improve its purity. Additionally, adsorbents have been used in the purification process. For example, Japanese Patent Kokai (laid-open) No. 5-1054 describes to the use of a hydrotalcite compound as the adsorbent.
To improve the color of .epsilon.-caprolactone, repetitious purifying distillation requires large distillation columns and a large amount of heat. Addition of a stabilizer is not satisfactory because it worsens the appearance of urethane resin produced from the lactone polyol. Use of a hydrotalcite compound as the adsorbent is expensive, and thus undesirable. Thus, conventional methods for the purification of .epsilon.-caprolactone are unfavorable, and the present invention offers significant improvement for obtaining purified .epsilon.-caprolactone.